GB2286792A

GB2286792A - Punching pliers

Info

Publication number: GB2286792A
Application number: GB9503344A
Authority: GB
Inventors: Harald Kohlmann; Ernst Pocksteiner
Original assignee: Dietzel GmbH
Current assignee: Dietzel GmbH
Priority date: 1994-02-23
Filing date: 1995-02-21
Publication date: 1995-08-30
Also published as: ATA37294A; DE19505613A1; AT400544B; GB9503344D0

Description

1 PUNCHING PLIERS 2286792 The present invention relates to punching pliers

for punching openings, in particular into distribution boxes made of plastics.

The construction business predominantly uses embedded boxes and tubings made of plastics for laying electric installations. While boxes embedded in plaster do not necessarily have to be liquid-proof, for boxes to be embedded in concrete it is necessary that the embedded box as well as the junction to the tubing is liquid-proof, as the intrusion of grout would make the arrangement useless. The opening diameters of the embedded boxes must exactly match the respective tube diameter. For economic reasons, embedded boxes have to be variably usable, i.e. offer the possibility to provide openings with the same or different diameters in various positions thereon.

Fig. 1 shows an exploded view of a typical example for a variably usable distribution box or device junction box, consisting of a box fastening lid 1, a main part 2 of the box and a bottom part 3 of the box. These three parts are sealingly connectable with each other by means of snap seats, and several box main parts are also sealingly snapablewithin each other at the tube stubs 4,5. The bottom and the main parts of the box have several areas 6, 7, 8, which are meant for providing openings for connection with a tubing. The tube stubs 4,5 are closed by plastic areas on the inside as well. The necessary openings cannot be cut with a knife or the like, as they normally have to be circular with an exactly defined diameter. Thus they are conveniently punched, the punching usually being done directly on the construction site by means of punchinpliers.

An example for such punching pliers is shown in Figs. 2a-2c. These conventional ph-i- consist of a V-shaped body 10 connected with grip elements 11, 12, each of which ac-as a single-armed lever, by means of hinges 13,14. One leg of V-shaped body 10 and the extension of grip element 11 beyond hinge 13 serve as pliers jaws on whl:,--,punching inserts 15, 16 are mounted. The punching inserts 15,16 take the form of circular hollow cylinders of constant height with an open top. During punching, when 2 the pliers grips are pressed together, grip element 12 exerts a force on the back of grip element 11, by which grip element 11 with punching insert 16 is pushed over punching insert 15 in a circarc movement around hinge 13.

These known pliers have severe disadvantages. Because of the circarc movement of the pliers jaw punching insert 16 is not pushed in parallel over insert 15, but the two inserts enclose an angle a at the first point of contact (shown in Fig. 2b). This means that the wall of the box for building-in is not cut perpendicularly, but obliquely at angle a, which strictly speaking does not produce a circular but an elliptical opening. As.the cylindrical punching inserts are not coaxially but obliquely inserted one into the other, the outer insert must have an inner diameter considerably greater than the outer diameter of the inner insert, so that inserting one into the other does not result in jamming. This in turn means that there has to be a distance between the cutting edges, which results in a piece of material being squeezed out undefinedly and not being cut during punching. This results in openings having frayed edges which do not form a sealed connection with tubes that are pushed in.

The axes of the cylindrical punching inserts only coincide after the pliers have been completely closed, as shown in Fig. 2c.

As the openings are sequeezed out of the wall made of plastics, large forces requiring long lever arms are necessary. Thus the length of the grip elements of the illustrated pliers is about 20 cm, the distance 1 between the grip ends when they are opened is about 18 cm, which is why handling with one hand becomes difficult.

The present invention aims at avoiding the above problems and at providing universaliy utilizable punching pliers that are easy to handle and can be produced inexpensively.

The punching pliers according to the invention are characterised by two doublearmed levers hingediy connected at a fulcrum as grip elements, each of which has two 3 additional hinge points positioned at opposite sides of the fulcrum, each one of these hinge points forming a fixed hinge with a hinge point of one of two pliers jaws, and the respective other hinge point of the double- armed levers forming a hinge displaceable in a guide with a second hinge point of the respective pliers jaw, the pliers jaws being moveable towards each other in parallel during punching and the two pliers jaws bearing punching inserts in the form of a punching knife or a punching sleeve at those sides facing each other.

Pliers having double-armed levers as grip elements and pliers jaws guided in parallel are known from riveting technology and thus relate to a technical field other than punchihg technology.

An embodiment of the invention having particular importance in practice is characterised in that the four hinges linking the grip elements with the pliers jaws are arranged at equal distances from the fulcrum connecting the grip elements, and in that the guidings are formed in such a way that during punching each of the displaceable hinges is guided along a straight line going through the two hinges of a pliers jaw. If the hinges have unequal distances from the fulcrum, the displaceable hinges have to be guided on curved paths so that parallel movement of the pliers jaws can be enforced, the guiding paths being bent towards each other as viewed in the direction of movement of the displaceable hinges when pressing the pliers together if the distance between the displaceable hinges and the fulcrum is smaller than the distance between the fixed hinges and the fulcrum, and the guiding paths being bent away from each other if the distance between the displaceable hinges and the fulcrum is larger than the distance between the fixed hinges and the fulcrum.

Guiding of the displaceable hinge along a straight or a curved path may conveniently be provided for in such a way that either in the grip element or in the pliers jaw a slot or oblong hole is formed, in which a pivot pin protruding through the slot or oblong holle as well as through the grip element is inserted in sliding fit so that the pivot pin is 4 displaceable in the slot or oblong hole. The use of an oblong hole as compared to a slot has the advantage that the forces occuring at right angles to the direction of displacement on punching can be better absorbed and bending or breaking of the material can be effectively prevented.

The punching inserts of the punching pliers according to the invention can have such a configuration that the punching knife has the form of a cylinder with at least one, preferably two inclined planar or continuously curved cutting edge(s), and the punching sleeve has the form of a hollow cylinder without top, the inner diameter of the punching sleeve being meant to have the size of the outer diameter of the cylindrical punching knife plus a tolerance, so that the punching knife may immerge in the punching sleeve in loose fit. By appropriately choosing the number of cutting edges of the punching knife and their inclination and curvature, respectively, the force gradient to be applied by manual pressure during punching can be influenced. By way of the hollow cylinder without top usable as punching sleeve, the plastic portions punched out can be ejected during punching already. Depending on the process tolerances determined for the remaining parts of the pliers, the dimensional tolerances of punching knife and sleeve can be determined as well. In a state of insertion, however, a loose fit should result.

Favourably, the pliers path is set in such a way that during punching the remaining way of the pliers jaws towards each other still is the wall thickness of the punching surface of the box to be built in plus an additional 1-2 mm after the cutting edge end set furthest to the rear has penetrated into the medium to be punched, in particular plastics. Thus it is made possible that smooth cutting edges in the plastic are always produced on punching, even though in particular soft plastic tends to flow upon being cut.

In order to enable universal utilization of the punching pliers according to the invention, the punching knife and/or the punching sleeve are to be arranged removably in the pliers jaws. Thus one pair of pliers can be adapted to tube diameters of various standards.

F One variant of this embodiment of the invention is characterised in that the punching knife and/or the punching sleeve is/are insertable in the pliers jaws in a defined position only, in particular by positive fit of a surface provided on a shank with a surface provided in a through hole or blind hole in the pliers jaws.

The grip elements and pliers jaws may be made of metal, e.g. aluminum or a Zn-Alalloy, or of plastics, e.g. glass fiber reinforced polyamide.

One embodiment of the present punching pliers is characterised in that at least one"of the pliers jaws is cranked in the direction towards the other pliers jaw or has a raised part as a seat of the punching insert.

It is also convenient for at least one of the pliers jaws to be at least partly camfered or to taper beginning from the side of the punching insert to the opposite side. By this configuration introducing and withdrawing of the pliers at locations of the box for building-in where access is difficult, as may result e.g. from reinforcing ribs or undercuts, is considerably facilitated.

For handling of the pliers it turns out to be practical if at least one tension spring!s mounted between a pliers jaw and a grip element for returning the punching pliers into the opened position.

The invention will now be described by way of example with reference to the drawings, wherein Fig. 1 is an exploded view of a plastic box for building into concrete, Figs. 1-1,, 2b, 2c are side views of conventional punching pliers in open, half-closed and fu'!"-.closed position, Figs. 3 and 4 show an embodiment of the punching pliers according to the invention in open and closed position in side view, Fig. 3a is a variant of th. embodiment of Fig. 3, Fig. 5 is a cross-section along line A-A in Fig. 3 of pliers ia"j with the punching knife turned by 90% Figs. 6a,6b, 6c show a section of the pliers jaw 6 receiving the punching knife of Figs. 3,4 in longitudinal view and in plan view, Figs. 7a, 7b, 7c are various embodiments of punching knives in side view, Figs. 8a,8b show a section of the pliers jaw receiving the punching sleeve of Figs. 3,4 in plan view and in longitudinal view, and Figs. 9a and 96 are perspective views of a punching sleeve and a punching knife.

Fig. 3 shows an embodiment of the punching pliers according to the invention in side view. It consists of two identical grip elements 20,20' bifurcated at one end, crossing each other at fulcrum M and hinged to each other. Hinging is done by means of a pivot pin fitted into through holes of the bifurcated parts of the grip elements and held in position by securing rings (not shown). Each of grip elements 20,20' has two more hinge points W,G2 and G1,W, respectively, situated on opposite sides of fulcrum M. One hinge point G1,Gl' each forms a fixed hinge with a bore of a pliers jaw 21,22, by inserting a pivot pin through the bore in the pliers jaw and the bores in the grip elements at hinge point G1,W, which pivot pin is secured against slipping out by means of a securing ring (not shown).

The other hinge point G2,W' arranged on the opposite side of fulcrum M forms a displaceable hinge together with an oblong hole 29,30 of the respective other pliers jaw by way of a pivot pin protruding through bores in the grip element and through the oblong hole and cooperating with the oblong hole in sliding fit.

A variant of this embodiment of the invention is shown in Fig. 3a. This embodiment differs from that shown in Fig. 3 only in that grip elements 20,20' have reinforced regions 40,41,42,43 around hinges Gl,G1',G2,G2', so that stronger forces can be taken up.

Pliers jaw 21 carries a punching sleeve 23 fixed by screw 27, and pliers jaw 22 carries a punching knife 24 fixed in the pliers jaw by screw 27. The punching knife and the punching sleeve will be detailed below. It can be seen that pliers jaw 22 has a raised k M 7 part 25 in the direction towards pliers jaw 21, which raised part carries punching knife 24. The end 26 of of pliers jaw 22 is camfered. Both construction measures serve for facilitating the insertion and withdrawal of pliers jaw 22 at locations of a box for building-in where access is difficult. The complete pliers arrangement is biased in the opened position by means of a spiral spring 28. The grip elements and pliers jaws may be made of metal, e.g. aluminum or a Zn-Al-alloy, or of plastics, e.g. glass fiber reinforced polyamide; the punching inserts 23,24 normally consist of metal, in particular steel.

The punching inserts are removeable, as shown in Figs. 6a-6c and Figs. 8a, 8b. Fig. 6a is a longitudinal view of a section of pliers jaw 22. A cylindrical through hole 31 flattened on one side 35 (see Fig. 6c) is provided for receiving the punching knife. Flattened wall portion 35 is provided so that a punching insert having positive fit may only be inserted in a defined position. Furthermore provision is made for a threaded bore 32 into which a screw 27 (Fig. 3) may be screwed in for fixing the punching insert.

The positive connection between punching insert and pliers jaw becomes particularly clear by referring to Fig. 9b, which shows a perspective view of punching insert 24. A cylindrical shank 44 having a flattened portion 45 on one side serves for receiving pliers jaw 22. Shank 44 is inserted in receptacle 31, the diameters of shank 44 and receptacle 31 being substantially the same and faces 35 and 45 corresponding with each other.

Fig. 6b is a longitudinal section of an alternative embodiment of pliers jaw 22. A cylindrical blind hole 33 also having a flattened wall is provided for receiving the punching knife.

Fig. 6c is a plan view of pliers jaw 22, partly in section, which corresponds to the representation of Fig. 6a. It can be seen that a definite position of insertion for the punching knife is predetermined.

8 Figs 7a-7c show various embodiments of cylindrical punching knives inserted in pliers jaw 22 and fixed with a screw -17.

Punching knife 24 has two opposing flat inwardly inclined cutting sides. It is important for all embodiments of the punching knife that the lowest point 34,34',34" of a cutting edge side is still moveable by a distance composed of the wall thickness of the plastic and a further tolerance path of 1-2 mm after it has entered the plastic, in order to guarantee a smooth cutting rim even wiffi plastics tending to flow. Fig. 7b shows an embodiment of a punching knife 24' having four inwardly inclined cutting edges offset from each other at angles of 90'. Fig. 7c shows a punching knife 24" having a curved cutting edge, which results in a constant gradient of the force to be applied from the first penetration of the cutting tip to complete separation of the punching part. The punching knives illustrated are provided in various standardized punching diameters.

Fig. 8a is a plan view, partly in section, of the receptacle of the removeable punching sleeve 23 in pliers jaw 21. Fig. 8b shows the same arrangement in longitudinal view. Punching sleeve 23 consists of a hollow cylinder made of steel without top, the inside diameter of which is somewhat larger, e.g. by 0,2-0,4 mm, than the outside diameter of punching knife 24,24',24", so that the sleeve and the inserted punching knife form a loose fit. Punching sleeve 23 is received in the pliers jaw 21 in a through hole 37 having an enlarged radius at the inner side of the pliers, which serves as a seat for collar 38 going round the outer peripheral surface of the sleeve. The sleeve is fixed in the through hole by means of a screw 27' that may be screwed into threaded bore 36. The arrangement described offers the advantage that punching chips are pressed out of the sleeve during punching already and do not have to be removed afterwards. Fig. 9a shows punching sleeve 23 with collar 38 in perspective view.

Fig. 5 shows a cross-section through pliers jaw 22 along line A-A of Fig. 3. As compare.' to the embodiment of Fig. 3, however, the double-edged punching knife 24 is turned by 901 in Fig. 5.

a 9_ 9 Referring to Figs. 3 and 4, functioning of the punching pliers according to the invention will now be described. When the two grip elements 20,20' are pressed against each other, pliers jaws 21,22 are moved towards each other as grips 20,20, act as doublearmed levers. At the same time the pivot pins in the oblong holes 29,30 are shifted as the changing distance between hinge points G1,G2 and GV,G2', respectively, are compensated for. As the longitudinal axis of the oblong holes coincides with straight lines between the points G1,G2 and GV,G2', respectively, pliers jaws 21, 22 execute an exactly parallel movement towards each other until they have reached the closed pliers position shown in Fig. 4, and punching knife 24 and punching sleeve 23 are coaxially inserted into each other.

The invention has been explained by way of an exemplary embodiment wherein hinges G1,Gl' are fixed hinges and hinges G2,G2' are displaceable hinges. Reversion of this arrangement of hinges is however conceivable as well. In the same way the oblong holes may be formed in the grip elements and the corresponding bores provided in the pliers jaws.

- 10 '

Claims

1. Punching pliers for punching openings, in particular into boxes made of plastics, characterised by two double-armed levers hingedly connected at a fulcrum (M) as grip elements (20,20% each of which has two additional hinge points (G] ',G2 and G 1,G2', respectively) positioned at opposite sides of the fulcrum (M), each one of these hinge points (Gl, G1') forming a fixed hinge with a hinge point of one of two pliers jaws (21,22), and the respective other hinge point (G2,G2') of the double- armed levers forming a hinge displaceable in a guide (29,30) with a second hinge point of the respective pliers jaw, the pliers jaws being moveable towards each other in paral.lel during punching and the two pliers jaws bearing punching inserts in the form of a punching knife (24, 24',24") and a punching sleeve (23), respectively, at those sides facing each other.

2. The punching pliers according to claim 1, characterised in that the four hinges (G l,G2,Gl',G2) connecting the grip elements with the pliers jaws are arranged at equal distances from the fulcrum (M) connecting the grip elements, and in that the guides have straight guiding paths, which, on punching guide each of the displaceable hinges (G2,G2') along a straight line passing through the two hinges of a pliers jaw (G1,G2 and Gl', G2', respectively).

3. The punching pliers according to claim 1, characterised in that the distance between the fixed hinges (Gl,G1') and the fulcrum (M) differs from the distance between the displaceable hinges (G2,G2') and the fulcrum (M), and in that the guides of the displaceable hinges have curved guiding paths compensating the angular displacement of the pliers jaws during punching, the guiding paths being bent towards each other as viewed in the direction of movement of the displaceable hinges when pressing the pliers together if the distance between the displaceable hinges (G2,G2') and the fulcrum (M) is smaller than the distance between the fixed hinges (Gl,G'."j and the fulcrum (M.... and the guiding paths being bent away from each other if the distance between the A j displaceable hinges (G2,G2') and the fulcrum (M) is larger than the distance between the fixed hinges (G 1,G V) and the fulcrum (M).

4. The punching pliers according to any of claims 1 to 3, characterised in that the guide takes the form of an oblong hole in the grip element or in the pliers jaw, in which a pivot pin of the displaceable hinge (G2, G2') protruding through the grip element and the pliers jaw is moveable in loose fit.

5. The punching pliers according to any of claims 1 to 4, characterised in that the punching knife has the form of a cylinder with at least one, preferably two inclined planar or continuously curved cutting edge(s) and the punching sleeve has the form of a hollow cylinder without top.

6. The punching pliers according to claim 5, characterised in that the inner diameter of the punching sleeve has the size of the outer diameter of the cylindrical punching knife plus a tolerance, so that the punching knife may immerge in the punching sleeve in loose fit.

7. The punching pliers according to any of claims 1 to 6, characterised in that during punching the remaining way of the pliers jaws towards each other still is the wall thickness of the box for building-in plus an additional 1-2 mm after the cutting edge end set furthest to the rear has penetrated into the medium to be punched, in particular plastics.

8. The punching pliers according to any of claims 1 to 7, characterised in that the. punching knife and/or the punching sleeve islare removably arranged in the pliers jaws.

0

9. The punching pliers according to claim 8, characterised in that the punching knife and/or the punching sleeve is/are insertable in the pliers jaws in a defined position only, 12- in particular by positive fit between a face (45) provided on a shank (44) and a face (35) provided in a through or blind hole in the pliers jaws.

10. The punching pliers according to any of claims 1 to 9, characterised in that the grip elements and the pliers jaws are made of metal, e.g. aluminum or a Zn-Al-alloy.

1.1. The punching pliers according to any of claims 1 to 9, characterised in that the grip elements are made of plastics, e.g. glass fiber reinforced polyamide.

12. The punching pliers according to any of claims 1 to 11, characterised in that at least one of the pliers jaws is cranked in the direction towards the other pliers jaw or has a raised part as a seat of the punching insert.

13. The punching pliers according to any of claims 1 to 12, characterised in that at least one of the pliers jaws is at least partly camfered or tapers beginning from the side of the punching insert to the opposite side.

14. The punching pliers according to any of claims 1 to 13, characterised in that at least one tension spring is mounted between a pliers jaw and a grip element for returning the punching pliers into the opened position.

15. Punching pliers substantially as described herein with reference to Figures 3 to 9 of the accompanying drawings.